Not applicable.
Not applicable.
The present invention relates to log handling equipment in general and to chain conveyors in particular.
After logs which are being processed for paper pulp or engineered wood products such as strandboard are debarked in a debarker, a chain conveyor is often used to transport the logs from the debarking drum to a flaker or other equipment for further processing. A chain conveyor has a plurality of chains, constructed of pivotal links which are drawn by a plurality of sprockets mounted on a drive shaft over the deck of a conveyor. At the drive sprockets the chains pass under the conveyor deck returning to the beginning of the conveyor where they pass over idler wheels and again begin their travel over the deck of the conveyor. As the conveyor chains wear, the chains become longer because the pins become smaller and the openings which the pins fit into become larger. Over time the excess chain hangs in a catenary under the conveyor. From time to time links can be removed from the chain, but the slack under the conveyor requires the conveyor to be elevated above the ground.
One known solution is to use two additional pulleys in a S-wrap configuration to take up the slack. The additional pulleys may be manually adjusted so as to take up the slack. Keeping slack to a minimum in the conveyor chains is important because, although the chains are normally driven in only one direction, if logs become jammed on the conveyor it is necessary to run the conveyor in reverse, and sometimes back and forth until the jam is broken. When the drive system is reversed, the drive shaft is no longer pulling on the loaded chain but pulls on the slack chain on the underside of the conveyor. The chains which are unloaded because of the slack may jump the sprockets, resulting in substantial cost and time expenditures, if not actual damage to the conveyor. One known solution is to replace the idler wheels with a second drive shaft and sprockets and a second drive system. However the additional drive shaft and drive system, while only used intermittently, substantially increase the cost of the chain conveyor. What is needed is a chain conveyor which can be mounted low to the ground and which does not develop slack in the conveyor chains.
The chain conveyor of this invention has an idler shaft to which idler wheels are mounted. The shaft is mounted to a carriage which is mounted to a frame for sliding motion along the direction of the chain conveyor bed. Hydraulic cylinders extend between the frame and the carriage and are constantly supplied with hydraulic oil at relatively low pressure such as can be developed with ordinary shop air pressure applied to an oil reservoir. When the conveyor is driven in the normal direction, the relatively low hydraulically applied stretching action removes slack from the conveyor chains by moving a carriage containing the idler shaft on idler wheels away from the drive shaft, increasing the length of the conveyor bed. The hydraulic lines supplying fluid to the hydraulic cylinders have check valves which only allow hydraulic fluid into the cylinders, thus allowing the cylinders only to move the carriage on which the idler shaft is mounted away from the drive shaft. When the chain conveyor is momentarily reversed, the entire loaded weight of the conveyor is now applied to the idler shaft, however the check valves prevent hydraulic fluid from leaving the hydraulic cylinders thus preventing any motion of the carriage. Much like a boa constrictor, the chain is tightened when there is little resistance to tightening, and the chain is held tightened when heavily loaded.
It is an object of the present invention to provide a chain conveyor in which slack is removed from the returning path of the chains without having depth to the conveyor structure.
It is another object of the present invention to provide a chain conveyor which can be driven in both directions, without the cost of two drive systems.
It is a further object of the present invention to provide a low-cost hydraulic system which supports large loads.